This invention relates to multifilament yarn of crimped bicomponent filaments and to a process for preparing it. The invention is more particularly concerned with yarn of crimped filaments composed of side-by-side polymeric components which will split apart in fabric finishing operations to provide improved fabric properties.
Bulky yarn has been prepared by melt-spinning two synthetic polymers to form a yarn of bicomponent filaments wherein the two components have different shrinkage properties, drawing and then heat relaxing the filaments to form a yarn of crimped filaments. For most purposes this product does not have sufficient advantages over conventional textured yarn of monocomponent filaments to justify the expense of producing bicomponent filaments. Breen et al. U.S. Pat. No. 3,017,686 discloses, in Example I and FIGS. 11 and 13, bicomponent filaments having a central portion of polyethylene terephthalate and two fins of polyhexamethyleneadipamide. The cross section of each fin has a width to thickness ratio of about 7 to 1, and the fin is lapped over the polyethylene terephthalate central component to give additional adhesive strength, as shown in FIG. 13 of the patent. When heat relaxed in boiling water, the central portion shrinks more than the fins and causes the fins to convolute helically about the central portion to give about 30 ruffles per inch of the type shown in FIG. 11.
Tanner U.S. Pat. No. 3,117,906 (or No. 3,181,224) discloses bicomponent filaments having rounded cross-sectional contours wherein a polyethylene terephthalate component and a polyhexamethyleneadipamide component are in temporary adhering side-by-side relationship along the length of the filament. As illustrated in Example I, when fabric containing the filaments is scoured at about 100.degree. C. while being vigorously flexed, the two components split apart as shown in FIG. 5. After drying and heat-setting at 400.degree. F. (204.degree. C.), the filaments are crimped as shown in FIG. 6. The crimp is of low order. Similar disclosure is found in Breen U.S. Pat. No. 3,117,362.
Nishida U.S. Pat. No. 3,917,784 also discloses bicomponent filaments having rounded cross-sectional contours wherein one component is polyethylene terephthalate and the other component is polyhexamethyleneadipamide. As the filaments are melt-spun, a non-aqueous oil composition is applied prior to the conventional aqueous spin finish to protect the filaments from splitting prematurely. After drawing, the filaments are permitted to relax in ambient air to develop spontaneous crimp. The filaments are split by immersing them in water at a temperature lower than 50.degree. C. and then raising the temperature higher than 80.degree. C. Loss of spontaneous crimp during the latter step can be avoided by packing the filaments in a vessel during treatment or, alternatively, the filaments may be used in fabric, then heat set and thereafter treated to split the components.